May 11, 2011 -- Pregnant women who have lower levels of the hormone oxytocin may be at greater risk for developing postpartum depression, a new study shows.

Sometimes called the "cuddle hormone" or the "hormone of love," oxytocin has been the subject of much research interest for its ability to foster feelings of bonding and attachment.

Previous studies have also suggested that oxytocin is important in parenting behaviors.

New fathers who are given a whiff of oxytocin nasal spray, for example, are more likely to encourage their children to explore during playtime and are less likely to be hostile, compared to fathers given a placebo.

Mothers with higher oxytocin levels are more likely to coo to their babies in a playful, squeaky voice, a kind of speech scientists call "motherese." They also tend to smile more at their infants and are more apt to respond to changes in the baby's mood with positive, loving touches or happy facial expressions than mothers with lower oxytocin levels, says James F. Leckman, MD, the Neison Harris Professor in the Child Study Center at Yale University in New Haven, Conn.

But the new study is one of the first to explore the relationship between oxytocin levels during pregnancy and the risk for postpartum depression, a condition that affects as many as one in five women.

"I think this particular finding needs to be replicated," says Leckman, who was not involved in the study. But if it is, a test for oxytocin may one day help to identify mothers at risk for depression after the birth of a baby.

"It's really an unfolding story," he says.

Oxytocin and Risk of Postpartum Depression

Researchers at the University of Basel, Switzerland, measured oxytocin levels in 73 healthy pregnant women. Sixteen reported previous episodes of major depression that had ended at least two years before they joined the study.

Blood samples to measure oxytocin were taken during the third trimester of pregnancy.

The women were given written screening tests to assess their risk of depression during pregnancy and again within two weeks of giving birth.

Overall, 14 women were determined to be at risk for postpartum depression based on their test scores. The risk of depression was not different between mothers who were breastfeeding and those who were not.

Lower oxytocin levels before birth were associated with a greater risk of postpartum depression.

"It may have some predictive value in terms of the mood state of the parent," Leckman says.

Other experts found the study interesting, but said important caveats applied.

Previous studies, for example, have suggested that changing oxytocin levels may have the greatest impact on mood, but this study only measured the hormone once, says Curt A. Sandman, PhD, professor emeritus in the department of psychiatry and human behavior at the University of California, Irvine.

"Also, there is an interest in sensitive periods during pregnancy when hormones may be particularly influential. This could not be assessed in this study," Sandman says.

Additionally, Sandman says, two weeks after birth may be a bit soon to assess depression risk since it's not uncommon for women to be moody as hormone levels readjust to pre-pregnancy levels.

Still, he tells WebMD, "There is a small literature about prenatal hormonal risk for PP [postpartum] depression and this adds to it and as such is a valuable contribution."

The study is published in the journal Neuropsychopharmacology.

Symptoms of Postpartum Depression

Many women experience a period of moodiness and stress after giving birth. If this doesn't go away after a few weeks, however, experts say it's important to seek help since children of depressed mothers are more likely to develop social and emotional problems of their own.

Signs of full-blown postpartum depression include lack of interest or negative feelings toward the baby, lack of self-concern, loss of pleasure, lack of energy or motivation, changes in appetite or weight, trouble sleeping, and thoughts of suicide.